1. Field of the Invention
This invention relates to an improved method and apparatus for determining, in real time, the position of the tip of an invasive probe inside a three-dimensional object and displaying its position relative to a geometrical model of that object visually displayed on a computer screen. More specifically, this invention relates to an improved method and apparatus of interactively determining the position of a probe tip inside the head of a patient during intracranial surgery relative to a three-dimensional internal diagnostic image of that patient.
2. Description of the Prior Art
Computed tomography (CT), magnetic resonance imaging (MRI), and other methods provide important detailed internal diagnostic images of human medical patients. However, during surgery there often is no obvious, clear-cut relationship between points of interest in the diagnostic images and the corresponding points on the actual patient. While anomalous tissue may be obviously distinct from normal healthy tissue in the images, the difference may not be as visible in the patient on the operating table. Furthermore, in intracranial surgery, the region of interest may not always be accessible to direct view. Thus, there exists a need for apparatus to help a surgeon relate locations in the diagnostic images to the corresponding locations in the actual anatomy and vice versa.
The related prior art can be divided into art which is similar to the present invention as a whole and art which is related to individual components of this invention.
Prior art similar to the present invention as a whole includes methods of correlating three-dimensional internal medical images of a patient with the corresponding actual physical locations on the patient in the operating room during surgery. U.S. Pat. No. 4,791,934 does describe a semi-automated system which does that, but it requires additional radiographic imaging in the operating room at the time of surgery as the means to correlate the coordinate systems of the diagnostic image and the live patient. Furthermore, the system uses a computer-driven robot arm to position a surgical tool. In particular, it does not display the location of an input probe positioned interactively by the surgeon.
There have been other attempts to solve the three-dimensional localization problem specifically for stereotactic surgery. One class of solutions has been a variety of mechanical frames, holders, or protractors for surgery (usually intracranial surgery). For examples see U.S. Pat. Nos. 4,931,056; 4,875,478; 4,841,967; 4,809,694; 4,805,615; 4,723,544; 4,706,665; 4,651,732; and 4,638,798. Generally, these patents are intended to reproduce angles derived from the analysis of internal images, and most require rigidly screwing a stereotactic frame to the skull. In any case, these methods are all inconvenient, time-consuming, and prone to human error.
A more interactive method uses undesirable fluoroscopy in the operating room to help guide surgical tools (U.S. Pat. No. 4,750,487).
More relevant prior art discloses a system built specifically for stereotactic surgery and is discussed in the following reference:
David W. Roberts, M.D., et al; "A Frameless Stereotaxic Integration of Computerized Tomographic Imaging and the Operating Microscope", J. Neurosurgery 65, October 1986. PA1 Fuchs, H.; Duran, J.; Johnson, B.; "Acquisition and 10 Modeling of Human Body Form Data", Proc. SPIE, vol. 166, 1978, pp. 94-102. PA1 Mesqui, F.; Kaeser, F.; Fischer, P.; "Real-time, Non-invasive Recording and 3-D Display of the Functional Movements of an Arbitrary Mandible Point", SPIE Biostereometrics, Vol. 602, 1985, pp. 77-84. PA1 Yamashita, Y.; Suzuki, N.; Oshima, M. "Three-Dimensional Stereometric Measurement System Using Optical Scanners, Cylindrical Lenses, and Line Sensors", Proc. SPIE, vol. 361, 1983, pp. 67-73.
It reports how a sonic three-dimensional digitizer was used to track the position and orientation of the field of view of a surgical microscope. Superimposed on the view in the microscope was the corresponding internal planar slice of a previously obtained computed tomographic (CT) image. The major disadvantages reported about this system were the inaccuracy and instability of the sonic mensuration apparatus.
Although the present invention does not comprise the imaging apparatus used to generate the internal three-dimensional image or model of the human patient or other object, the invention does input the data from such an apparatus. Such an imaging device might be a computed tomography (CT) or magnetic resonance (MRI) imager. The invention inputs the data in an electronic digital format from such an imager over a conventional communication network or through magnetic tape or disk media.
The following description concentrates on the prior art related specifically to the localizing device, which measures the position of the manual probe and which is a major component of this invention. Previous methods and devices have been utilized to sense the position of a probe or object in three-dimensional space, and employ one of various mensuration methods.
Numerous three-dimensional mensuration methods project a thin beam or a plane of light onto an object and optically sense where the light intersects the object. Examples of simple distance rangefinding devices using this general approach are described in U.S. Pat. Nos. 4,660,970; 4,701,049; 4,705,395; 4,709,156; 4,733,969; 4,743,770; 4,753,528; 4,761,072; 4,764,016; 4,782,239; and 4,825,091. Examples of inventions using a plane of light to sense an object's shape include U.S. Pat. Nos. 4,821,200, 4,701,047, 4,705,401, 4,737,032, 4,745,290, 4,794,262, 4,821,200, 4,743,771, and 4,822,163. In the latter, the accuracy of the surface sample points is usually limited by the typically low resolution of the two-dimensional sensors usually employed (currently about 1 part in 512 for a solid state video camera). Furthermore, these devices do not support the capability to detect the location and orientation of a manually held probe for identifying specific points. Additionally, because of line-of-sight limitations, these devices are generally useless for locating a point within recesses, which is necessary for intracranial surgery.
The internal imaging devices themselves (such as computed tomography, magnetic resonance, or ultrasonic imaging) are unsuited for tracking the spatial location of the manually held probe even though they are unencumbered by line-of-sight restrictions.
A few other methods and apparatus relate to the present invention. They track the position of one or more specific moveable points in three-dimensional space. The moveable points are generally represented by small radiating emitters which move relative to fixed position sensors. Some methods interchange the roles of the emitters and sensors. The typical forms of radiation are light (U.S. Pat. No. 4,836,778), sound (U.S. Pat. No. 3,821,469), and magnetic fields (U.S. Pat. No. 3,983,474). Other methods include clumsy mechanical arms or cables (U.S. Pat. No. 4,779,212). Some electro-optical approaches use a pair of video cameras plus a computer to calculate the position of homologous points in a pair of stereographic video images (for example, U.S. Pat. Nos. 4,836,778 and 4,829,373). The points of interest may be passive reflectors or flashing light emitters. The latter simplify finding, distinguishing, and calculating the points.
Probes with a pointing tip and sonic localizing emitters on them have been publicly marketed for several years. The present invention also utilizes a stylus, but it employs tiny light emitters, not sound emitters, and the method of sensing their positions is different.
Additional prior art related to this patent is found in these references:
The paper by Fuchs, et al., (1978) best describes the method used by the present invention to track the surgical probe in three-dimensional space. It is based on using three or more one-dimensional sensors, each comprising a cylindrical lens and a linear array of photodetectors such as a charge-coupled semiconductor device (CCD) or a differential-voltage position sensitive detector (PSD).
The sensors determine intersecting planes which all contain a single radiating light emitter. Calculation of the point of intersection of the planes gives the location of the emitter. The calculation is based on the locations, orientations, and other details concerning the one-dimensional sensors and is a straightforward application of analytic geometry. This electro-optical method, however, has not been previously used for the purpose of the present invention.
Thus, there still remains a need for a complete apparatus which provides fast, accurate, safe, convenient mensuration of the three-dimensional position of a manual probe and which visually relates that position to the corresponding position on the image of a previously-generated three-dimensional model of an object.